如何在UIAlertController的中心显示活动指示器? [英] How to display activity indicator in center of UIAlertController?

问题描述

我当前在屏幕上显示UIAlertController.警报的视图应仅在警报的中心显示2个元素，即标题和UIActivityIndicatorView.下面是显示警报及其元素的功能.

I currently have a UIAlertController being displayed on the screen. The view of the alert should only display 2 elements, a title and a UIActivityIndicatorView in the center of the alert. Below is the function that displays the alert and its elements.

func displaySignUpPendingAlert() -> UIAlertController {
        //Create the UIAlertController
        let pending = UIAlertController(title: "Creating New User", message: nil, preferredStyle: .Alert)
        //Create the activity indicator to display in it.
        let indicator = UIActivityIndicatorView(frame: CGRectMake(pending.view.frame.width / 2.0, pending.view.frame.height / 2.0, 20.0, 20.0))
        indicator.center = CGPointMake(pending.view.frame.width / 2.0, pending.view.frame.height / 2.0)
        //Add the activity indicator to the alert's view
        pending.view.addSubview(indicator)
        //Start animating
        indicator.startAnimating()

        self.presentViewController(pending, animated: true, completion: nil)
        return pending
    }

但是，活动指示器不会显示在视图中心，实际上它显示在屏幕的右下方，离视图很远.是什么原因呢?

However, the activity indicator doesn't display in the center of the view, in fact it displays in the bottom right of the screen, far off of the view. What is the reason for this?

我知道我可以为指示器的位置硬编码数字，但是我希望警报可以在具有多种屏幕尺寸和方向的多种设备上运行.

I understand that I can hardcode numbers for the indicator's position, but I want the alert to work on multiple devices with multiple screen sizes and orientations.

推荐答案

创建视图时，请务必设置frame属性.

Be sure to set the frame property when you're creating a view.

func displaySignUpPendingAlert() -> UIAlertController {
        //create an alert controller
        let pending = UIAlertController(title: "Creating New User", message: nil, preferredStyle: .Alert)

        //create an activity indicator
        let indicator = UIActivityIndicatorView(frame: pending.view.bounds)
        indicator.autoresizingMask = [.flexibleWidth, .flexibleHeight]

        //add the activity indicator as a subview of the alert controller's view
        pending.view.addSubview(indicator)
        indicator.isUserInteractionEnabled = false // required otherwise if there buttons in the UIAlertController you will not be able to press them
        indicator.startAnimating()

        self.presentViewController(pending, animated: true, completion: nil)

        return pending
}

致@ 62Shark:

To @62Shark:

let pending = UIAlertController(title: "Creating New User", message: nil, preferredStyle: .Alert)

let indicator = UIActivityIndicatorView()
indicator.setTranslatesAutoresizingMaskIntoConstraints(false)
pending.view.addSubview(indicator)

let views = ["pending" : pending.view, "indicator" : indicator]
var constraints = NSLayoutConstraint.constraintsWithVisualFormat("V:[indicator]-(-50)-|", options: nil, metrics: nil, views: views)
constraints += NSLayoutConstraint.constraintsWithVisualFormat("H:|[indicator]|", options: nil, metrics: nil, views: views)
pending.view.addConstraints(constraints)

indicator.userInteractionEnabled = false
indicator.startAnimating()

self.presentViewController(pending, animated: true, completion: nil)

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